Drawbacks of Rutherford Atomic Model
Let us first understand about the basics of Rutherford Atomic model. Before discussing the advantages and disadvantages it is very necessary to understand the basics of Rutherford atomic model.
Initially JJ Thomson presented the plum in a pudding model in which electrons were present in the atom like plum in a pudding. Sir Ernest Rutherford refuted this model to its very core. He conducted the experiment with the use of Gold foil and alpha particles. In this experiment the gold foil was bombarded with alpha particles. To Rutherford’s surprise most of the particles passed straight through the foil. He has a zinc scintillator placed at the back of the foil in order to see scintillations. While most of the particles passed through the foil, some were diverted at an angle of more than 90 degrees, while a very few were reflected back at 180 degrees. This was a very shocking finding because this suggested that most of the mass and hence the charge is present and concentrated in the middle of the atom. This charge is present in a very small region. This was because not many particles were deflected, most of them passed through the gold foil. Also most of the mass of the atom was concentrated in the middle. This region was then called nucleus.
There were many shortcomings or drawbacks of Rutherford atomic model. They are as follows –
- Rutherford did not mention any direct link between the charge of the nucleus and the atomic mass. He did not mention whether this was half or more than that of atomic mass.
- He did not mention the relation between charge of the nucleus and atomic number.
- It was later confirmed that the charge on the nucleus and the atomic number are exactly the same entities.
- Rutherford model did talk about ‘most’ of the atomic mass (the central nucleus) but did not say anything about the remaining of it.
- Rutherford did not talk about the rest of the atomic mass and about the exact positioning of electrons. His model just stated that electrons may be arranged in rings (As in Hydrogen ). But this was already stated in JJ Thomson model and hence was nothing new.
- Also as per Rutherford’s model electrons are charged particles revolving round the nucleus like planets around the sun in solar system. They do so in a circular motion. But if this was true then electrons would also experience acceleration as any other particle revolving in a circular orbit would do. This would lead to energy loss and electrons will fall in nucleus which will in turn cause the atom to be highly unstable. This is false. We know today and knew before that atom is stable.
These shortcomings were the reason for the upcoming new model that is the Bohr’s model of Atom. Bohr model clearly talked about the positioning of electrons in the atom etc. Rutherford experiment with the gold foil also proved that the alpha particles were never affected by the presence of the electrons in the atom. Till now it was realized that atom is a single particle but in subsequent years it was proved by experiments that atom is basically made up of much smaller particles. These particles are today known as neutrons, electrons and protons. Neutrons and protons make up most of the nucleus. Out of this neutrons are mass less and they have neutral charge. However th